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Balanced QDV

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Balanced QDV

Unread postAuthor: killerbanjo » Tue Nov 12, 2013 10:35 pm

This can be done MUCH more efficiently but the same theory applies. Was checking my laptop and found this pic from a while ago and though I would upload it. The bolt needs revising to be effective and it might work better with a moving barrel to be honest...

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EDIT: Revised some small mistakes
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Re: Balanced QDV

Unread postAuthor: killerbanjo » Wed Nov 13, 2013 12:11 am

I have now revised my old design into a simpler one. The chamber is no long a jacket' to the valve which allows the balanced piston to be shortened reducing dead space, the piston was also thickened to increase weight (Hopefully slower fire rate) and decrease dead space. The Barrel is also part of the piston and moves in blowback action. The valve is de-balanced but pushing back on the barrel via a piece soldered/welded on.

Due to the design if you held back the trigger the valve would stay open and dump all your air, so a screw is fitted to the trigger so that a sweet spot can be set, allowing for automatic fire by always stopping the valve from fully closing but a tiny amount.

Image

I'm eager for your opinions!
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Re: Balanced QDV

Unread postAuthor: Technician1002 » Wed Nov 13, 2013 6:53 am

There is no reason to vent the piston, so you can eliminate the large diameter and 3rd O ring. This reduces size, weight, and complexity. Air mass dumping in front of the piston is enough to pop it open if the friction is low. Use floating o rings for the required low friction. If you can achieve a piston mass near the mass of the projectile, the piston will be able to open fully with only a small amount of travel of the piston and projectile. Reduce the length of the piston to reduce dead space and further reduce mass.
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Re: Balanced QDV

Unread postAuthor: killerbanjo » Wed Nov 13, 2013 8:40 am

Thanks for the information, assuming what I have drawn is correct however does give it a downfall. On the old design it would snap open much quicker and also the magazine was completely sealed off before it shot, this way it is not delayed therefore air would be lost.

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Re: Balanced QDV

Unread postAuthor: POLAND_SPUD » Wed Nov 13, 2013 11:26 am

if what you want is a mechanically triggered spudgun/piston you should focus on an unbalanced QDVs not balanced ones
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